1. Field of the Invention
This invention relates to a light equipment using a semiconductor light-emitting device array, particularly to a light equipment used for LED printer, laser printer, laser display, image sensor or the like.
2. Description of the Related Art
Conventional LED printers use as a light equipment a multi-tip head obtained by, as illustrated in FIG. 11, connecting rectangular LED light-emitting device chips Ch1 and Ch2 in a row, each of said chips having light emitting points LP arranged in one dimension.
Various methods have so far been proposed to attain high-density device arrangement. For example, proposed in Japanese Published Unexamined Patent Application No. Hei 2-147259 is a method in which chips having thereon light emitting points arranged in the staggered form are formed and then these chips are connected each other. In this method, light emitting points are arranged in the staggered form within one chip, which widens the distance between the two adjacent light emitting points and also widens the interconnection space, thereby bringing about an improvement in the yield. The end surface of the chip to be connected is parallel to the subsidiary scanning direction (the direction corresponding to the rotational direction of a drum in the surface of the LED chip) so that with an increase in the density of the light emitting points, the end surface of the chip becomes closer to the light emitting point. The distance between the end surface of the chip and the light emitting point include a margin of a predetermined value as shown in FIG. 12 because of the problem of the positional accuracy caused by chip cutting. It is necessary to provide several .mu.m or greater for the distance between the light emitting point and the end surface to be cut in consideration of the damage caused by cutting. The scatter in the positional accuracy caused by chip cutting is .+-.5 .mu.m or greater so that the scatter in the distance between the end surface and the light emitting point becomes 5-15 .mu.m. If it is 15 .mu.m, the distance between light emitting points becomes 30 .mu.m when chips are connected, which makes it impossible to actualize a pitch of 21 .mu.m for 1200 dpi.
In addition, disclosed in Japanese Published Unexamined Patent Application No. Hei 5-94080 is an optical head in which two rows of light-emitting devices are disposed, each of said devices being formed of an array light source obtained by successively connecting chips, and said two rows are disposed so that image formation points are arranged in a straight line on a photo-sensitive drum through rod lenses respectively corresponding to these two rows. It is only necessary to install, in each row, a light emitting point array having a light emitting point density half of the recording density. Owing to such low light emitting point density, the above optical head can be actualized easily. But, it is almost impossible to precisely align image formation points of each row from one end of the drum surface to the other end. In practice, it is very difficult to satisfy the severe demand for positional accuracy of light emitting points on the order of microns and moreover, this method is impractical because it takes a tremendous time and cost for the fabrication.
Moreover, Japanese Published Unexamined Patent Application No. Sho 59-164161 discloses a light-emitting diode array head in which the end surface of a semiconductor chip to be connected, said chip having light emitting diode rows which have been divided into at least two blocks in order to facilitate easy position control upon the connection of the light-emitting diode chips, is inclined at 5.degree. from the original angle 90.degree. relative to the light emitting diode rows.
By the technique described above, it becomes easier to carry out position control upon chip connection. If the light emitting diode rows are divided into two or more blocks, the electrode interconnection should be disposed on one side. In such a case, the higher the arrangement density of light emitting points, the higher the interconnection density, which makes it difficult to conduct wire bonding or the like. Accordingly, the above method is accompanied with the problem that it cannot be applied to a light emitting device array having a high light emitting point density. Besides, the blocks should be arranged in the staggered form from the viewpoint of the space of electrode interconnection of each block and it is substantially difficult to arrange the blocks in three or more lines. The above method is therefore accompanied with the problem that light emitting points cannot be two-dimensionally arranged freely.
As described above, in the conventional semiconductor device array of a multi-chip structure, the higher the device arrangement density in the chip connecting direction, the closer the distance between the end surface of the chip to be connected and the semiconductor device. Under the present situations, an error in the position accuracy caused by chip cutting or an error in the position accuracy caused by chip bonding is at least several .mu.m so that when the cut end surface of the chip is vertical to the chip connecting direction, it is impossible to actualize the chip connection with light emitting points being arranged at high density such as 1200 dpi. Furthermore, when the device arrangement density becomes higher, it becomes impossible to secure an interconnection space or wire bonding space in the one-dimensional arrangement of light emitting points. Accordingly, there is a demand for the two-dimensional arrangement of light emitting points, thereby widening the distance between the light emitting points.